You know, for how rewarding the 3stacks mechanic is most of the time...

I'm surprised they aren't restricted to just auto attacks or abilities applying stacks most of the time.

Deals 6-14% max HP in magic damage (everything else in his kit is physical) and he gets a burst of movement speed to disengage or chase.

Deals 4-10% max HP, has a 20% armor shred, and gets 30-50% bonus attack speed

Deals magic damage, applies spell effects, dishes out a 30-60% slow for 2-3 seconds, and gets a nice movement boost

For how much of a power spike these give the champs and how strong a trading tool they are it's really frustrating when both their abilities and autos are applying stacks. Try to trade with in lane? autoed and boomeranged the second you get close, then all he has to do is land one more auto and hop away (or even just walk away because speed boost. Run across in the jungle? Q-auto-E reset auto and she's already hit the 3 stacks in under a second. finally manages to hit both parts of his Q? here comes his dash blink to land the third stack.

the 3stack mechanic DOES have an example of being only applied by abilities and it's on the champ a lot of people consider to be (one of) the most balanced in the game , he gets some flat true damage, and has to land 3 abilities, he can refresh the stacks with autos, but not get more, it feels like this is fairer. If Gnar and Vi had to actually land 3 auto attacks, they wouldn't just like, start any prolonged encounter roided up and already have chunked their opponent, and wouldn't win any short trades simply by virtue of being able to get 3 stacks in a second. Ekko is a little harder to split, since he's a far more hybrid champ in terms of ability-auto attack balance, it could be that simply having a single target cooldown is enough for him.